1. Field of the Invention
The present invention relates to an aircraft window and more particularly to a lightweight, glass and polycarbonate laminate for an aircraft windshield that reduces windshield deflection due to internal aircraft cabin pressure and reduces the load on the polycarbonate plies of the windshield.
2a. Technical Considerations
As an aircraft flies to higher altitudes, the air within the aircraft cabin is pressurized. As a result, the transparencies in the aircraft experience cyclic loading each time the aircraft's internal pressure changes in response to altitude changes. This cyclic loading on polycarbonate plies of the windows may lead to premature failure through fatigue. Because of the relatively low stiffness of polycarbonate as compared to other commonly used transparent material, the cyclic loading causes the polycarbonate plies of the transparency to deflect outwardly, changing the surface contour of the window as well as the entire aircraft. To reduce this deflection, a more rigid ply, for example a glass outer ply, may be incorporated into the laminated transparency. However, when the perimeter of the polycarbonate plies is restrained through attachment to an airframe, while under pressurization, center deflection of the polycarbonate will tend to cause the transparency to delaminate about its periphery, between the glass ply and the remaining polycarbonate plies of the transparency due to the more rigid glass deflecting less at the periphery.
It would be useful to have an aircraft transparency, and in particular an aircraft windshield, utilizing polycarbonate and glass plies that avoids these deleterious delamination effects while maintaining a structurally sound transparency capable of withstanding significant impacts that can occur to an aircraft windshield.
2b. Patents of Interest
U.S. Pat. Nos. 3,919,022 and 4,004,388 to Stefanik disclose a window panel edge construction for a glass laminate which includes molded, fiber glass reinforced, thermosetting resinous straps adhered to and overlapping both sides of the glass plies of the panels in a peripheral area outside the viewing area. During lamination, the straps cure to form rigid connecting members rigidly secured to the window glass plies and other edge materials.
U.S. Pat. No. 3,953,630 to Roberts et al. teaches a laminated transparent assembly which includes a glass laminate with polyvinyl butyral interlayers and a high tensile strength, flexible insert which extends around and has a portion embedded in the periphery of the interlayer. A portion of the insert which extends beyond the periphery of the transparency is used to mount the transparency to a vehicle.
U.S. Pat. No. 4,046,933 to Stefanik teaches a transparent laminated window which uses a flexible fabric tape impregnated with a silicone elastomeric adhesive to bond at least one of the plies or reinforcements of the window to another element of the window.